1. Field of the Invention
The present invention relates to a display device, and more particularly, to a display device with a built-in self-capacitive touch panel.
2. Discussion of the Related Art
With the advance of various portable electronic devices such as mobile terminals and notebook computers, the demand for flat panel display devices applied to the portable electronic devices is increasing.
In such FPD devices, the application fields of the LCD devices are being continuously expanded because the LCD devices are easily manufactured due to the advance of manufacturing technology and realize a drivability of a driver, a high-quality image, and a large screen.
Instead of an input device such as a mouse or a keyboard which is conventionally applied to LCD devices, a touch screen that enables a user to directly input information with a finger or a pen is recently applied as an input device to LCD devices.
As types in which a touch panel is provided at a liquid crystal panel, there are an on-cell type, an in-cell type, and a hybrid in-cell type. LCD devices using the in-cell type or the hybrid in-cell type are called LCD devices with a built-in touch panel.
FIG. 1 is an exemplary diagram illustrating a configuration of a related art LCD device, and FIG. 2 is an exemplary diagram showing a timing at which a common voltage and a driving pulse are applied to a touch electrode in the related art LCD device.
The related art LCD device with a built-in touch panel, as illustrated in FIG. 1, includes a liquid crystal panel 10 with a built-in touch panel 60 and a touch sensing unit 30 for driving the touch panel 60. A method of driving the touch panel 60 includes a resistive type and a capacitive type. The capacitive type is categorized into a self-capacitive type and a mutual type.
In the related art LCD device using the self-capacitive type of the types, as illustrated in FIG. 1, a touch electrode line 62 is separately extended from each of a plurality of touch electrodes 61, and “q×p=n” number of sensors 31 are needed in consideration of the number “q” of widthwise touch electrodes and the number “p” of lengthwise touch electrodes. When the number of sensors 31 is small, the touch sensing unit 30 itself may be configured as one integrated circuit (IC), and when many sensors are needed, a plurality of ICs (touch ICs) configured with a plurality of the sensors 31 may configure the touch sensing unit 30.
In the above-described LCD device with the built-in self-capacitive touch panel, since a touch electrode receiving a driving pulse is used as a common electrode, an output of an image and touch sensing cannot simultaneously be performed. Therefore, as shown in FIG. 2, one frame period determined by a vertical sync signal Vsync is divided into a display period and a touch sensing period.
Each of the sensors 31 applies ten or more driving pulses to the touch electrode 61 during the touch sensing period, and analyzes a sensing signal received from the touch electrode to determine whether a corresponding touch electrode is touched.
Generally, in the self-capacitive type, determining whether there is a touch uses charging or discharging of the driving pulse. That is, in the self-capacitive type, a touch is detected by using a voltage slope change caused by a change in a capacitance value which occurs between when there is a touch and when there is no touch
FIG. 3 is a graph for describing a method of determining a touch in a related art display device using the self-capacitive type.
In the self-capacitive type, a relaxation oscillation type is being widely used.
In the relaxation oscillation type, a sensing time is decided based on a self-capacitance value and the number of charging and discharging.
In the relaxation oscillation type, a time decided based on a self-capacitance value is counted with a clock generated from a reference oscillator.
In the relaxation oscillation type, a digital code value can be obtained by counting a decided time with a clock generated from the reference oscillator.
However, the relaxation oscillation type has a problem that it is difficult to determine whether there is a touch in an in-cell type touch panel.
The relaxation oscillation type is a very useful structure in a single self-capacitive type. However, a parasitic capacitance is generated between self-capacitances in the in-cell touch panel, and thus, when the same voltage is not provided, the parasitic capacitance value is greatly changed. For this reason, crosstalk occurs, and a unique value of the self-capacitance is changed, whereby it becomes difficult to determine whether there is a touch.
To provide an additional description, in the related art relaxation oscillation type, as shown in FIG. 3, a current is supplied to each of a plurality of touch electrodes to increase a voltage of each touch electrode to a predetermined touch voltage, and then whether there is a touch is determined by counting a time when the touch voltage is again dropped. The time when the touch voltage is dropped varies according to whether there is a touch, and thus, whether there is a touch may be determined by using a time difference. The above-described operation may be repeated several times for increasing the time difference. In FIG. 3, a method that counts the time when the operation is repeated four times is illustrated.
However, when a touch is made in plurality in a plurality of touch electrodes or a touch is made in one of a plurality of touch electrodes, touch electrodes adjacent to a touch electrode in which a touch occurs are affected by a capacitance change of the touch electrode in which the touch occurs. For this reason, an abnormal touch can be detected even in the adjacent touch electrodes.